Hydrothermal systems are responsible for the vast majority of economic metal deposits (e.g., skarn, porphyry, epithermal, mesothermal, and VMS deposits) and play a critical role in regulating the geochemical budgets of the oceans through time. Significant challenges remain in addressing key questions, including: (i) the sources of precious (e.g., Ag, Au) and base (e.g., Cu, Zn) metals in these systems; (ii) the processes, reaction rates, and mechanisms that optimize ore formation; (iii) strategies for identifying and exploiting the most economically favorable regions of hydrothermal systems; and (iv) the extent to which hydrothermal processes have influenced marine chemistry over geologic time.

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To address these questions, Dr. Antonelli developed a geochemical model demonstrating that paleoseawater chemistry exerts a strong feedback on the composition of ocean-floor hydrothermal vent fluids. This model shows that reduced seawater Mg and SO₄ concentrations lead to decreased release of basalt-derived Ca and Sr into the oceans, and that continental weathering fluxes—constrained by seawater ⁸⁷Sr/⁸⁶Sr—were likely lower than previously assumed during the Cretaceous and Ordovician (Antonelli et al., 2017, PNAS). Stable isotopes are also central to resolving these problems, as reactive kinetic isotope effects occur in both continental and ocean-floor hydrothermal systems and can be quantitatively linked to reaction rates, mechanisms, and mineral supersaturation states.

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In collaboration with C. Chelle-Michou (ETH Zurich), Antonelli is now investigating kinetic isotope effects during Pb–Zn and Fe skarn formation. This work reveals significant variability in calc-silicate precipitation rates between skarn-forming fluid pulses, which appear to correlate with crystal size distributions (Antonelli et al., AGU Conference, 2021). In parallel, he is involved in multiple projects, in collaboration with A. Giuliani and M. Schmidt, examining stable and radiogenic Ca isotope fractionations in kimberlites from ab initio (in collaboration with E. Schauble, UCLA), experimental (piston-cylinder centrifuge apparatus), and natural perspectives. These studies provide critical constraints on the petrogenesis of economically important mantle-derived melts.

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Although many ore deposits form through prolonged hydrothermal activity, a large fraction of economically significant mineralization results from rapid chemical reactions. As discussed in the review by Watkins and Antonelli (2021, Elements), reactive kinetic isotope effects associated with rapid, unidirectional processes offer powerful insights into the dynamics of ore-forming hydrothermal systems.